1. Field of the Invention
The present invention relates to an air conditioning control system that controls air conditions in an office, a hospital and the like, to a supply air switching controller for use in the air conditioning control system, and to an air conditioning control method.
2. Description of the Related Art
A heat sensation of a human body is affected by a plurality of factors such as a room temperature, an indoor humidity, a mean radiant temperature, an action quantity, a clothing quantity and an air velocity.
However, in usual, in a place in an office building, where persons are present, an air velocity is 0.1 m/s or less, and accordingly, the heat sensation is hardly affected thereby. Moreover, the clothing quantity is fixed by a season such as summer and winter, and the action quantity is determined to some extent by a type of a building in terms of use, such as the office building and a department store. Furthermore, the mean radiant temperature substantially follows the room temperature except on a window side.
Hence, when the above-described respective factors are examined, the humidity is the second factor that largely affects amenity of the persons after the room temperature.
FIG. 1 shows, as a range A, a combination of the room temperature and the humidity, which is defined so that an amenity index (predicted mean vote: PMV) in which the amenity of the persons is represented by a numerical value can stay within a comfortable range of 0.3 to 0.5 (in the case of considering to save energy at the time of cooling in summer).
As shown by this range A, the humidity is lowered to some extent, whereby the amenity can be obtained without lowering the room temperature more than necessary.
However, in actual, air conditioning control in many office buildings mostly performs only room temperature control, and the humidity is not taken into consideration at all.
A reason for the above is as follows. In the case of also attempting to control the humidity at such a cooling time, when air to be controlled is dehumidified, the air is cooled excessively by a cold water coil. Therefore, in order to adjust a supply air temperature, a process of a reheating cycle of the air in a heating coil becomes necessary. As a result, when the humidity is also attempted to be controlled at the cooling time, extremely large energy is consumed in comparison with the case of only the temperature control.
Accordingly, in order to solve such a problem as described above, an air conditioning control apparatus in which a direct expansion coil that dehumidifies outside air is added to an air conditioner has been proposed in Patent Publication 1 (Japanese Patent Laid-Open Publication No. 2006-292300).
As shown in FIG. 2, the air conditioner using a technology of Patent Publication 1 includes: a direct expansion coil 41 that introduces and dehumidifies the outside air; a cold/hot water coil 42 that cools return air from a room inside subjected to the air conditioning control and adjusts a temperature of supply air to the room inside; and a supply air fan 43 that supplies mixed air of the outside air dehumidified by the direct expansion coil 41 and the return air cooled by the cold/hot water coil 42 into the room inside subjected to the air conditioning control. As described above, in the air conditioner using the technology of Patent Publication 1, the dehumidification of the outside air and the cooling of the return air are performed independently of each other, whereby it becomes possible to perform air conditioning control, in which the amenity is maintained, while achieving energy saving.